The present invention relates generally to concrete, and more particularly to water permeable concrete systems.
Concrete is extensively utilized as a building material for industrial, commercial and residential applications. Due to its durability, wear resistance and cost economy, concrete has gained widespread use in walked upon and driven upon applications. Part of the problem when constructing aesthetically pleasing surfaces is that current design and engineering methods require the use of integrated surface drain systems to capture and channel away excess water, rain and run-off into drainage systems. However, they are visually detracting from the overall finish surfaces being placed and take-away from the natural look of some of the concrete or simulated natural materials one may be re-creating in concrete.
Pervious concrete, also commonly referred to as porous concrete, permeable concrete, and no-fines concrete, has been commonly used to effectively capture and divert storm water runoff. Pervious concrete is a special type of concrete having a high porosity that allows water and other liquids to pass directly through the concrete thereby reducing the runoff from a site. Typically, the water is diverted directly into the ground for introduction into the water table. Pervious concrete functions like a storm water infiltration basin and allows water to saturate soil over a large area, thus facilitating the introduction of water into the groundwater supplies locally. As a result, pervious concrete is recognized as a “Best Management Practice” by the United States Environmental Protection Agency.
Pervious concrete consists of cement, coarse aggregate and water, with little to no fine aggregates. The addition of a small amount of sand will increase strength, but decrease porosity. This may be desirable in cold climates where higher strength due to freezing is a concern. Typically, the water to cement ratio is 0.28-0.40 with a void content of 15%-25%. This results in the pervious concrete having a water flow rate of 2-18 gallons per minute per square foot.
Unfortunately, pervious concrete suffers from several disadvantages. Most notable is that the lower density results in significantly lower strength. Accordingly, pervious concrete is typically used in lower trafficked roadways, parkways, or walkways. Where higher traffic and durability is a concern, pervious concrete is typically not acceptable. Furthermore, depending on the region, the cost of pervious concrete may be 15%-25% higher than conventional impervious concrete. Due to these disadvantages, pervious concrete has faced difficulties in its adoption in the United States.
Various attempts have been made to create concrete structures which provide water porosity and improved characteristics. For example, U.S. Pat. No. 7,168,884 describes a paving structure which is water permeable. The structure includes an upper layer of blocks, and lower layers of coarse granular material, a geotextile membrane, a sub-base of gravel or concrete, and a subgrade below. Water is permitted to flow through this concrete structure. However, the structure is expensive and more difficult to build than traditional concrete structures. U.S. Pat. No. 5,788,407 also describes a paving structure which is water permeable. This structure includes two layers of water permeable concrete. Unfortunately, these layers of water permeable concrete lack the strength of conventional concrete. Meanwhile, U.S. Pat. No. 8,312,690 describes a pervious concrete structure. Again, the concrete structure includes an upper pervious concrete layer which may contain decorative aggregates. Below the decorative pervious concrete layer is an additional pervious concrete layer connected by an acrylic binder. Unfortunately, the impervious concrete layers lack the strength of conventional concrete.
Thus, there is a need for an improved concrete construction that allows for the drainage of water without the cost of integrated surface drainage systems. Furthermore, there is a need to provide a level flat top surface that is aesthetically pleasing which does not permit standing surface water. This would be a significant benefit for the advancement of the Americans with Disabilities Act (ADA) which requires certain characteristics of walking surfaces.
Moreover, there is a significant need for a pervious concrete system which has improved strength and durability compared to previous pervious concrete constructions.
Thus, there is a significant need for an improved a concrete paving system that creates a safer surface and is not detrimentally impacted by the design or engineering constraints utilizing traditional methods of paving surface drainage systems.